Computer Crime Research Center

PC clock as a fingerprint for your PC

Anyone is able to track and id a PC anywhere on the Internet by using its PC clock deviation as a fingerprint. Clock deviation is what a computer thinks the time is as compared to other time-keeping with which it is interfacing. And when measured against other quantifiable processes when the computer is connected to the Internet, it can apparently provide a reliable fingerprint, unique and allowing it to be tracked throughout the Internet.

"The clock deviation fingerprint" is based on the work of University of California graduate student Tadayoshi Kohno, who explains that clock deviation fingerprinting is based on the fact that typically "each party in a TCP flow includes information about its perception of time in each outgoing packet. A fingerprinter can use the information contained within the TCP headers to estimate a device's clock deviation and thereby fingerprint a physical device."

This, by the way, is all done without the knowledge or any cooperation from the owner of the Internet-connected device being tracked and fingerprinted by its clock deviation. Says Kohno, "For all our methods, we stress that the fingerprinter does not require any modification to or cooperation from the fingerprintee." Even more impressive when you consider that they have successfully used clock deviation fingerprints to track devices using just about every popular operating system, including Windows, OS X, Linux, FreeBSD, and even Pocket PCs.
Original article